As medical science delves into smaller areas of the body, such as blood vessels, it has become increasingly difficult to reach these areas with an effective conventional apparatus. In part, this is due to the materials from which the apparatus is made, and the dangers to the apparatus due to the methods of introduction into the body and in particular, the small areas of the body. Particularly, catheters having inflatable balloon attachments have been used for reaching these small and related areas, such as in coronary angioplasty. More particularly, stent delivery and placement devices useful for opening occluded or blocked vessels have been used in coronary and peripheral angioplasty, urology and reproductive surgeries, among others.
Balloon catheters are produced from materials that can sustain large amounts of pressure. However, the profile of balloon catheters and related devices must be small in order to be introduced into the small areas of the bodies, such as blood vessels. Therefore, materials with high strength relative to film thickness are chosen. An example of these materials is PET (poly-ethylene terephthalate), which is useful for providing a non-compliant, high-pressure device for delivering a stent to a vessel. Unfortunately, PET and other materials with high strength to film thickness ratios tend to be scratch and puncture sensitive. Polymers that tend to be less sensitive to scratches, such as polyethylene, nylon, and urethane are compliant, and at the same film thickness as the non-compliant PET, do not provide the strength required to withstand the pressure used for delivering a stent into a vessel wall. Non-compliance, or the ability not to expand beyond a predetermined size on pressure and to maintain substantially a profile, is a desired characteristic for balloon catheters, particularly for use in small vessels, so as not to rupture or dissect the vessel as the balloon expands. A layer added on the substrate may provide some protective characteristics to a medical apparatus by virtue of the added thickness, and many resins may be used for this purpose. However, such a physical barrier, provides only limited protection.
Further difficulties often arise in guiding a catheter into a desired location in a patient due to the friction between the apparatus and the vessel through which the apparatus passes. The result of this friction is failure of the balloon due to abrasion and puncture during handling and use and also from over-inflation. There has been attention in the field to providing lubricious coatings to the medical apparatus to diminish friction that causes apparatus failure. One such lubricious coating for balloon catheters is described in U.S. Pat. No. 5,272,012 to Opolski, wherein the use of a slip additive such as a siloxane is disclosed. These coatings improve the success rates of balloon catheters by altering the friction coefficient by use of lubricious coatings. However, they do not address the scratch and puncture-resistance of the apparatus other than by building film thickness, which is inadequate protection against destruction of the balloon by tears, scratches, punctures and the like, particularly for the delivery of stenting devices.